The present disclosure relates to a method of coating an internal surface of a component to enhance hot corrosion resistance. In particular, the present disclosure relates to a method of coating the internal surface of an airfoil to enhance hot corrosion resistance.
During operation of gas turbine engines, the temperatures of combustion gases may exceed 3,000° F., which is considerably higher than the melting temperatures of the metal parts of the engine, which are in contact with these gases. The metal parts that are particularly subject to temperature extremes and degradation by the oxidizing and corrosive environment, and thus require particular attention with respect to cooling, are the hot section components exposed to the combustion gases, such as blades and vanes used to direct the flow of the hot gases, as well as other components such as shrouds and combustors.
High and low pressure turbine airfoils are manufactured from nickel based super alloys. These components are protected against the high temperature environment by a thermal barrier coating (TBC). However, the internal surface of airfoil can be difficult to coat, therefore often susceptible to high temperature oxidation and material damage and loss in more corrosive environment.
Internal surface oxidation has been found to be responsible for airfoil performance deterioration due to blockage of the air passages in the trailing edge. This issue is particularly pronounced in countries where air pollution leads to high SO2 concentration and airborne particulate matters contains sulfate and phosphate in the atmosphere. Repairing the airfoil with internal oxidation damages involves rebuilding the wall and replenishment of elements that can form thermally grown oxides for protection. Traditional coating application techniques such as plasma spray, cathodic arc, electron beam physical vapor etc., are not suitable for coating the internal surface due to line of sight limitation.